1. Field of the Invention
The invention is related to the field of magnetic disk drive systems and, in particular, to patterned magnetic media and associated methods of fabrication. More particularly, the fabrication of patterned magnetic media is performed to define servo patterns in one or more arrays of islands that are formed using self-assembly materials.
2. Statement of the Problem
Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more sliders that include a read/write head. A suspension arm holds the slider above a magnetic disk. When the magnetic disk rotates, an air flow generated by the rotation of the magnetic disk causes an air bearing surface (ABS) side of the slider to ride a particular height above the magnetic disk. The height depends on the shape of the ABS. As the slider rides on the air bearing, an actuator moves the suspension arm to position the read/write head over selected tracks of the magnetic disk.
A conventional magnetic disk is divided into data regions and servo regions. The data regions are comprised of a plurality of data sectors where actual data is stored. In the data regions, the magnetic surface of the disk is divided into small magnetic regions, each of which is used to encode a single binary unit of information. The magnetic regions include a few hundred magnetic grains forming a magnetic dipole which generates a highly localized magnetic field. The read/write head magnetizes a magnetic region by generating a strong local magnetic field to store a bit of data.
The servo regions are comprised of a plurality of servo sectors that are used to assist in reading and writing to the data sectors, such as by positioning the read/write head over the center of tracks, deriving a synchronization signal, etc. When data recording is performed on a magnetic disk, the read/write head is positioned over the tracks based on a positioning signal (Positioning Error Signal (PES)) that is read from the servo sectors on the disk. The servo sectors include burst fields that are used to guide the read/write head to the proper position on the disk. There are typically four servo burst fields (also referred to as a quadrature burst) that are defined in the servo sectors. The servo burst fields are typically offset from one another in relation to the center of one or more tracks on the magnetic disk. Thus, depending on where the read/write head is positioned (i.e., center track or off track), the read/write head will read different signals from the servo burst fields. The resultant signals read from the servo burst fields are then processed, and a determination is made as to how far the read/write head is offset from the center of the track. Appropriate positional correction of the read/write head may then be performed. The servo sectors may also include synchronization fields, Automatic Gain Control (AGC) fields, and other fields.
As the areal density of the magnetic disk increases, the super-paramagnetic effect causes problems for disk manufacturers. The super-paramagnetic effect occurs when the microscopic magnetic grains on the disk become so tiny that ambient temperature can reverse their magnetic orientations. The result is that the bit is erased and the data is lost.
One solution to the problems posed by the super-paramagnetic effect is to pattern the magnetic disk. A patterned magnetic disk is created as an ordered array of discrete magnetic islands, with each island capable of storing an individual bit. Because each island represents an individual magnetic domain, the patterned magnetic disk is thermally stable and higher densities may be achieved.
One method used to pattern a magnetic disk is with self-assembly materials. Self-assembly materials are known as materials that uniformly order themselves due to their inherent properties. For entities (molecules, macromolecules, etc) interacting with potentials having cylindrical or spherical symmetry, hexagonal close packed (HCP) ordering is the most common ordering that is achieved with self-assembly. Self-assembly works best when the entire surface area of interest is completely covered.
There are problems encountered when fabricating patterned media with self-assembly materials. In data sectors, the islands of the patterned media should be uniformly spaced. The precise locations and sizes of the islands are important to the signal-to-noise ratio (SNR) and the Bit Error Rate (BER) of the data recording process. Also, to increase the areal density of the disk, the spacing and size of the islands have to be small. Self-assembly thus works well to form the data patterns as a well-ordered array of islands, such as an array having HCP ordering.
By contrast, the servo patterns in the burst fields and synchronization fields in the servo sectors do not conform easily to HCP ordering or other simple arrays, and some patterns rely on the existence of empty spaces in the pattern. Such servo patterns are difficult to achieve with self-assembly. Thus, it is a problem to pattern servo regions using self-assembly.